Abstract LB141: <i>In vivo</i> co-produced BTEs targeting FSHR and Her2 overcome ovarian cancer therapeutic resistance in mice

Abstract Ovarian cancer (OC) is a deadly disease in need of newer therapies. Several immunotherapy approaches including checkpoint inhibitors, cancer vaccines and CART cells have been explored for OC, with limited clinical success. Bispecific T cell engagers (BTEs) allow direct engagement of adaptive immunity, potentially making them important for OC. First-generation BTEs suffer from short half-lives, resulting in poor pharmacokinetics which reduces their effectiveness. BTEs also have complex manufacturing processes and stringent storage requirements, resulting in increased costs and potentially reducing accessibility and limiting patient uptake. Heterogeneity in expression of tumor associated antigens (TAAs) further complicates treatment with a single BTE, as OC can evade the immune impact of targeting a single antigen. Targeting multiple TAAs could enhance anti-tumor efficacy. We describe a novel approach by adapting Knob-into-hole technology into a DNA format designed for in vivo assembly and secretion of bivalent BTEs (dKBTEs). This unique approach allows for simplified multi-TAA targeting to overcome tumor heterogeneity. Two dKBTEs targeting FSHR (dK_FSHRxCD3) and Her2 (dK_Her2xCD3) were designed and tested. in vitro, both dKBTEs expressed at expected sizes, bound to their respective TAA and T cells and induced T cell effector functions. These dKBTEs demonstrated potent and specific cytotoxicity of several OC cell lines which are derived from tumors with different driver mutations and resistance to several approved therapies for OC. In mice, they showed superior pharmacokinetics and tumor control compared to first-generation BTEs. Combination therapy with both dKBTEs further improved tumor control over single dKBTE therapy. DNA delivery allows for in vivo production, assembly and secretion of BTEs without compromising expression or activity when codelivering two dKBTEs. This study demonstrates that in vivo codelivery of dKBTEs targeting multiple TAAs can better impact antigen heterogeneity and evasion, presenting a promising strategy for OC treatment. Citation Format: Pratik Sanjivkumar Bhojnagarwala, Devivasha Bordoloi, Joshua Jose, David B. Weiner. In vivo co-produced BTEs targeting FSHR and Her2 overcome ovarian cancer therapeutic resistance in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB141.